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The Familiar of Zero (ゼロの使い魔 Zero no Tsukaima?) is a fantasy and comedy-oriented series of Japanese light novels written by Noboru Yamaguchi, with illustrations by Eiji Usatsuka. Media Factory published the first volume in June 2004 and 20 volumes have been released as of February 2011. The story features several characters from the second year class of a magic academy in a fictional magical world with the main characters being the inept mage Louise and her familiar from Earth, Saito Hiraga.

Between 2006 and 2012, the series was adapted by J.C.Staff into four anime television series and an additional original video animation episode. The first anime series was licensed by Geneon Entertainment in English, but the license expired in 2011. A manga version drawn by Nana Mochizuki was serialized in Media Factory's manga magazine Monthly Comic Alive between August 2006 and October 2009. The manga is licensed by Seven Seas Entertainment for release in North America. Three additional spin-off manga were also created, as were three visual novels.

Louise is a noble girl who is terrible at magic, as her attempts usually result in an explosion. She is nicknamed "Louise the Zero" by her classmates, due to the inability to use any of the four magic elements. Early in the school year at the Tristain Academy of Magic, the second year students perform a special ritual where they summon their familiar, which serves as their eternal protector and partner, and is usually some sort of magical creature. But Louise summons Saito Hiraga, an ordinary teenage boy from Japan, leaving her totally humiliated.

Due to the sacredness of the ritual, Louise reluctantly accepts Saito as her familiar, but proceeds to treat Saito as any other familiar, only worse, making him wash her clothes, sleep on a bed of hay, and whipping him with a riding crop for little or no reason. The Familiar of Zero follows the adventures of Louise and Saito as they help their classmates and friends, while occasionally blundering into situations where they risk their lives to save one another. Saito tries to find a way to get back to Japan, but he also has a mysterious power that allows him to wield swords and other weapons to perform heroic feats. They also eventually learn the truth behind Louise's magic inabilities.

Halkeginia

Halkeginia (ハルケギニア Harukeginia?) is the continent that the story of The Familiar of Zero takes place on. Halkeginia's social structure is similar to the feudal class systems of Europe in the Middle Ages, with magic-users being considered nobles. The continent itself is vaguely reminiscent in shape of western Europe, with many of the countries carrying ancient and Roman names.

Tristain

Tristain (トリステイン Torisutein?, also "Tristein") is the nation in which the majority of the story takes place. It is a small monarchal country located in the northwest of Halkeginia. It is under threat from Albion. Tristain is home to a highly acclaimed magical academy which attracts students from nearby countries known as the Tristain Academy of Magic.

Militarily, the country is weak, with only a small permanent force, which forces it to make marriage alliances with other countries. The capital city is Tristania (トリスタニア Torisutania?).

Germania

Germania (ゲルマニア Gerumania?) is the largest kingdom in Halkeginia, and is also regarded as the strongest in terms of military might. It is regarded as a more barbaric and down-to-earth type of country, with its men considered to be brutish. Germania is located to the northeast of Tristain. Germania is the ancient Roman for the region that is now Germany, the natives were at the time considered by the Romans to be barbarians.

Gallia

Gallia (ガリア Garia?, also "Galia") is another kingdom in Halkeginia, located to the southeast of Tristania. Germania is on its eastern border, in the Alden Forest. It is the second largest country in Halkeginia. Within the Gallia Royal Family, murders and assassination attempts have led to an unstable royalty. There is a city named La Rochelle in the mountains, which is a major port. Gallia is reminiscent of modern day France, which in the Roman era was called Gaul.

Albion

Albion (アルビオン Arubion?), nicknamed the white country, is a floating island nation which is in a period of political strife. According to the storyline, a group of nobles known as Reconquista initiated a coup d'etat against the royalty, and over the course of the story, succeed in killing the entire Albion Royal Family. Cromwell, the leader of the Albion rebellion, seeks to spread his power elsewhere, and begins by attacking Tristain. Albion is the ancient Greek name for the main island of Great Britain upon which are the modern nations England, Wales, and Scotland.

Cromwell is named after the leader of the Roundheads during the English Civil War, Oliver Cromwell, who successfully ousted the Monarchy, and establishing a brief reign as Lord Protector until the return of Charles II.

Romalia

Romalia (ロマリア Romaria?) is a holy empire, located to the south of Gallia. Reminiscent of Italy, and specifically the Holy Roman Empire (and the Vatican City, it is mentioned, that they have a pope and officials who are bound to celibacy), which once formed northern Italy and much of central Europe.

A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host. Thus parasitoids are similar to typical parasites except in the more dire prognosis for the host.

Definitions and distinctions

The term parasitoid was coined in 1913 by the German writer O. M. Reuter (and adopted in English by his reviewer, William Morton Wheeler) to describe the strategy in which, during its development, the parasite lives in or on the body of a single host individual, eventually killing that host, the adult parasitoid being free-living. Since that time however, the concept has been variously generalised and widely applied.

In practice it is not always necessary to distinguish parasitoidy from parasitism, nor is it always even possible to do so cleanly. However, when it is appropriate to do so, a typically parasitic relationship is one in which parasite and host interact without lethal harm to the host, and without dramatically reducing the host's reproductive success. In most such relationships, the parasite arrogates enough nutrients or other resources to thrive without preventing the host from reproducing. In contrast, in a parasitoidal relationship the exploiting organism kills or sterilises the host, typically before it can produce offspring. A non-lethal parasite sometimes is termed a biotroph. In contrast, when a parasitoidal relationship is regarded as a form of parasitism, the parasitoid may be called a necrotroph.

When an organism sterilises its host without directly killing it, then whether to term it a parasitoid or a parasite, is a matter of context and preference. Often for a parasite to prevent reproduction of the host is incidental, but various forms of systematic parasitic castration occur among parasitoids, and many such biological strategies are highly sophisticated. Crustacean parasites or parasitoids include several impressive examples.

Protelean is a term that various authors use to denote organisms that live as parasites only during the early, growing, phases of their lives; typically they then begin by behaving as internal parasites; also typically they end that phase of their lives parasitoidally by killing or consuming the host. Finally they emerge as free-living adults, with or without an intervening phase of diapause or metamorphosis.

Protelean organisms are widely regarded as a special class of parasites, or more usually parasitoids. The most typical examples of proteleans are the parasitoidal Hymenoptera, Diptera, Strepsiptera, and some other insects. Usually such insects are holometabolous. It is reasonable to regard holometaboly as preadaptation for the protelean life history because it implies that their larval stage of life differs drastically from the adult stage, both functionally and morphologically.

Idiobiont parasitoids are those that prevent further development of the host after initially immobilizing it, and, almost without exception, develop outside the host. Koinobiont parasitoids allow the host to continue its development while feeding upon it, and may parasitize any host life stage. In turn, koinobionts can be subdivided further into endoparasitoids, which develop inside body of the host, and ectoparasitoids, which develop outside the host body, though the parasitoids frequently are attached or embedded in the host's tissues.

It is fairly common for a parasitoid itself to serve as the host for another parasitoid's offspring. The latter is commonly termed a hyperparasite, but in most cases this term is slightly misleading, as both the host and the primary parasitoid are killed. A better term might be secondary parasitoid, or hyperparasitoid.

Most known specialist hyperparasite and hyperparasitoid species are in the insect order Hymenoptera, but a fair amount of incidental hyperparasitoidy results when a single host or a single food stash happens to house multiple guests and rations run short. Some members of the flesh fly family, Sarcophagidae, subfamily Miltogramminae, for example members of the genus Craticulina, are kleptoparasites of wasps in the subfamilies Bembicinae and Philanthinae (both currently placed in the family Crabronidae). Both those subfamilies tend to build nests by digging tunnels in sand, which they then stock with prey such as flies or bees, depending on the species. Kleptoparasitic flies such as Craticulina are much smaller than the host wasp and lay their eggs on the prey as the wasp returns to the nest on a victualing flight. The fly larvae are small, though faster-growing than the wasp larva, and if there is only one, the wasp is likely to complete its metamorphosis successfully, but when there are several it might suffer from malnutrition or even get eaten itself, which amounts to incidental kleptoparasitoidy.

In contrast though, as described in the following section, some insects, such as some members of the Trigonalidae, not only are specialist hyperparasitoids, but have advanced behavioural adaptations to support their speciality.

Note once again that there is no clear separation between the concepts of parasitism and parasitoidy. Many species of true parasites can cause the death of their host if for example they are present in overwhelming numbers or the host is in poor condition, or other compromising circumstances develop, such as secondary infections. For example, blood-sucking mites sometimes overwhelm nestlings of birds such as swallows to the point that the young birds cannot fledge successfully

Infestations of other mites cause various kinds of mange in mammals. Mange mites are generally in the families Demodicidae that cause Demodicosis or demodectic mange, Sarcoptidae that cause scabies or sarcoptic mange, and Psoroptidae that cause scab in sheep and rabbits. Severe mange can debilitate animals to the point that they cannot feed themselves adequately, so that in unfavourable circumstances they may die.

Again, various species of paralytic ticks sometimes kill dogs if the owners are insufficiently alert, and soft ticks can fatally poison a host such as a horse that might rest in an infested shady spot because it does not know the local hazards. Conversely, some parasitoids do somewhat shorten the lives of their hosts or constrain their reproduction, but without necessarily killing them as a part of their interaction. Almost any microbial disease could be defined as a parasitic condition, and some could be argued to amount to clear examples of parasitoidy. One converse argument is that when the death of the host is neither a logical nor necessarily even a desirable consequence from the point of view of the parasite, the relationship should be regarded as parasitic rather than parasitoidal. This certainly would apply to examples such as mange, and diseases in which the living victim acts as a natural reservoir or even a vector.

In their extreme forms the categories of parasitism and parasitoidy patently are distinct; one is in no doubt whether the larva of a Tarantula hawk wasp behaves more like a parasitoid, or even a predator, than a parasite; and similarly the biting midges that suck blood from large insects plainly are simply ectoparasites. However, there is a continuum of intermediate and contingent conditions that bridge those categories in practically every respect. This should not be taken too seriously as a material problem in terminology; the terms are useful in particular contexts and should not be abused by inappropriate application in contexts in which they create confusion rather than clarity. Many examples of species that are technically parasitoidal, at least facultatively, are not generally referred to as parasitoidal. Many microbial diseases and the aforementioned soft ticks constitute instructive examples.

Nor do those complete the list of examples that constitute the requirement for fuzzy distinctions in such matters; at the opposite extreme from parasitism, parasitoidy in turn grades into predation. Differences between various kinds of hunting wasps provide convenient illustrations. Predatory social wasps hunt flies, caterpillars and the like, grab them, butcher them, carry them home and feed them to their young. That is patent predation. Some solitary wasps, such as bee pirates, sting prey, sometimes fatally, before saving it, usually entire, in a nest or burrow for the young to feed on. That too is predation, fairly clearly.

In contrast, the best-known protelean solitary hunting wasps sting prey to paralyse it before storing it for the young in the nest. The larvae then proceed to eat the stored prey alive, sometimes according to very sophisticated schedules that delay killing the victim sooner than necessary, thereby avoiding having their rations rot before they could be consumed. Some authorities regard such larval behaviour as having a strong element of parasitoidy. That view is based largely on the view that the young larvae begin with small exactions like any parasite, then proceed to the point where they eat at such a rate that they might as well be predators.

Other wasps paralyse prey in the plant or other environment in which it feeds, before laying eggs nearby. The emerging young attack and feed on the paralysed prey organism in its own home. Some solitary parasitoids among insects lay their eggs on or in their live prey and any of a wide range of consumption schedules might follow. Some parasitoids even lay their eggs where the larvae must locate the prey for themselves when they hatch from the eggs. Examples include flies in the families Tachinidae and Bombyliidae. The physiological and strategic sophistication of such relationships, whether parasitoidal or parasitic, often are impressive.

Patently there is no point to trying to draw arbitrary lines of distinction between such vague, and often variable, life histories. In each ecological or ethological study the terms applied should reflect the facts in the contexts relevant to the matter in question. Such studies need not in all cases use the identical terminology, and there is no reason they should. All that is necessary is that the terminology in each study should be clear, useful and relevant.

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Types of parasitoids

The parasitoidal type of relationship seems to occur largely in organisms that have fast reproduction rates, such as insects or (perhaps more rarely) mites or nematodes. Workers in this field have pointed out that parasitoids often are closely coevolved with their hosts, which is inarguably true. To maintain a sound perspective of the matter though, one must remember that coevolution might reasonably be expected to develop to even higher degrees of sophistication in the more intimate classes of parasitic relationships. In fact advanced degrees of coevolution occur in the complex interplay between simultaneously extant predator-prey relationships as well.

In using the term parasitoid it is common to think in terms of parasitoidal insects such as Tachinidae and Pompilidae. Some writers recognise or discuss no other classes of parasitoidy. More realistically however, the life histories of several other groups of organisms are equally parasitoidal. In general there is no logical basis for excluding wider use of the term. For example, among the so-called worms, many Nematoda are important parasitoids of insects, snails and similar commercially important pest organisms. Under favourable circumstances they commonly multiply in the host until the carcase is a shell overflowing with a pullulating mass of worms.

Other organisms that might merit the term include certain Pteromalid gall wasps that abort host plant inflorescences, seed weevils, certain plants largely regarded as parasitic, and certain bacteria and viruses (e.g., bacteriophages), in relationships where the beneficiaries obligately destroy their hosts.

Not all such organisms regularly behave quite so parasitoidally of course; for example some bacteriophages establish complex life cycles in which phage particles do get released catastrophically, but only at intervals of many generations of the host, whereas other bacterial viruses emerge intermittently but fairly harmlessly in small numbers at a time.

The clearest cases of fully functional parasitoidy are the likes of many parasitoidal wasps and flies that consume their hosts as completely as any spider or hawk that summarily eats its prey. However, there also are many species of parasitoid that frequently or even routinely kill their "host" or "prey" without consuming much of it. This apparently wasteful strategy sometimes might have the effect of reducing the risk that the prey could escape or offer resistance. In other cases the residue of the victim simply might be difficult to eat or not very nutritious. For example various Phorid flies such as Apocephalus species, are parasitoids of particular species of ants. Various species attack ant genera such as "big-headed ants", "Fire ants" or Solenopsis, Paraponera, and leaf-cutter ants. However, the larvae of most such Phoridae eat mainly the contents of the ants' "head capsules" abandoning the rest of the carcases when pupating. In laying her eggs, the parent fly selects the largest ant workers, which have just the size of head to produce an adequate adult phorid. Presumably the large head-capsule contains the most concentrated nutritious muscle and brain tissue. One also could think of the Rabies virus in similar terms, or the aforementioned soft ticks. Both commonly or invariably cause the death of the host, after consuming at most a trivial fraction of the host's resources.

Influence on host behaviour

In another strategy, some parasitoids influence the host's behaviour in ways that favour the propagation of the parasitoid, often at the cost of the host's own life. A spectacular example is the endoparasitoid Dicrocoelium dendriticum, the Lancet Liver Fluke that causes host ants to die clinging to grass stalks where grazers or birds may be expected to eat them and complete the parasitoidal fluke's life cycle in its definitive host. Similarly, as strepsipteran parasitoids of ants mature, they cause the hosts to dawdle high on grass stalks, positions that are risky, but favour the emergence of the Strepsipterans. Other species of endoparasitoids cause infected woodlice and land Amphipoda such as Talitroidesto run about in the open by day, where predators such as birds can catch them and continue the cycle.

Returning to the case of the rabies virus and the disease, one could rationalise the death of the host similarly. The virus affects the host's central nervous system with eventually fatal effects. That could be seen as a consequence of the strategy for dissemination of the virus by affecting the host behaviour. Similar principles might apply to, for example, Vibrio cholerae, the cholera bacterium and other, often fatal, enteric pathogens that induce diarrhoea and spread by contagion.

For the soft ticks the benefit of the paralysis they inflict might be seen as influencing behaviour in that it prevents the host from wandering away while they feed, which they do very quickly and in large numbers, some species emerging from their hiding places at night. Other species hide in sandy patches in the shade of trees in semi-desert such as the Kalahari, and emerge to feed as soon as any large animal settles down in the shade during the heat of the day.

In parasitic birds such as cuckoos, the young often are adapted to act as "super solicitors", with loud, persistent voices and with large, vividly coloured gapes and behaviour that stimulate the feeding instincts of the foster parents to the utmost. Consequently the legitimate chicks, even if they are not evicted, often starve because they are less well-equipped for soliciting for food.

Parasitoidal microbial diseases

As mentioned, some microbial parasitoids waste most of the host's resources when it dies, but there are other parasitoidal strategies among microbes as well. One more conceptually economical form of parasitoidy is exemplified by microbial pathogens of various invertebrates such as many insects. The most notorious might well be Microsporidiosis in the form of nosema in silkworms. This infection is highly virulent and the tissues of the victims contain huge numbers of infectious spores. In effect the pathogen in its role of parasitoid has used up most of the resources of the host to propagate and spread its offspring. Similarly, many viruses, bacterial and other, continue to propagate inside a host cell until it physically ruptures. In doing so they too consume effectively the whole of the host's resources.

Parasitoidal fungi such as Entomophthora species carry this principle as far as is possible. Having infected and killed an insect, they continue to grow on the carcase and release spores for as long as any resources remain. In this such microbes resemble the aforementioned propagation of some Nematoda in snails and insects.

Parasitoidal plants

There are parasitoidal plants as well. Various species of dodder indiscriminately parasitise wide ranges of host plants, and debilitate or kill the branches that they infect, and commonly the whole host plant as well.

Mistletoes in families such as Santalaceae and Loranthaceae commonly accumulate on host trees till they stunt and eventually kill them, sometimes after many decades. Occasionally a freak condition can arise where the (strictly speaking "hemiparasitic") plant can supply sufficient photosynthetic power to support the root system of a small host tree for several years after the live host shoots have effectively disappeared.

A related example is where the parasitoid plant is not strictly a parasite in the normal sense, but nonetheless exploits the host's resources of space, support and light. The best-known are the so-called "strangler figs". Some of them will grow on and round the trunk of the host tree and squeeze it or starve it of light until, after perhaps decades, it dies. The strangler eventually replaces the host utterly as the original trunk rots from within the stems of the strangler, leaving a hollow framework.

Parasitoidal crustaceans

The subphylum Crustacea includes a surprising range of parasitoidal species and strategies. As with many other parasitoids, the killing of the host often is incidental. For example, in the family Ergasilidae, the "gill lice", most adult females live as parasites in the gills of fish. The harm they do the host is incidental to the parasitism, but it often is fatal or at least debilitates the fish so badly as to prevent breeding.

A particularly startling genus of Cirripedia, or barnacles is Sacculina. It literally injects itself into a crab of a suitable species and by complex processes converts itself into an egg-laying bag. In the process it disrupts the reproductive system of the host, an act of parasitic castration that qualifies it for classification as a parasitoid rather than just a parasite.

Those examples are just a few of many among the Crustacea.

Parasitoidal insects

*Braconidae Wasp Cocoons On Giant Leopard Larva.

About 10% of described insect species are entomophagous parasitoids.[18] There are four insect orders that are particularly renowned for this type of life history. By far the majority are in the order Hymenoptera.

The largest and best-known group comprises the so-called "Parasitica" within the Hymenopteran suborder *Apocrita: the largest subgroups of these are the chalcidoid wasps (superfamily Chalcidoidea) and the ichneumon wasps (superfamily Ichneumonoidea), followed by the Proctotrupoidea and Platygastroidea. Outside of the Parasitica, many other Hymenopteran lineages that include parasitoids, such as most of the Chrysidoidea and Vespoidea, and the rare Symphytan family Orussidae.

The flies (order Diptera) include several families of parasitoids, the largest of which is the family Tachinidae, and also smaller families such as Pipunculidae, Conopidae, and others. Other families of flies that are not primarily parasitoids or parasites, or at least not primarily protelean, do nonetheless include protelean species. For example Phoridae have already been mentioned as parasitoidal on ants, and at least some flesh fly species, such as Emblemasoma auditrix, are parasitoidal on cicadas, and have raised great interest because they locate their hosts by sound. The kleptoparasitic flesh fly genus Craticulina has already been mentioned and logically qualifies as a protelean fly genus.

Two other orders with parasitoidal members are the "twisted-wing parasites" (order Strepsiptera), which is a small group consisting entirely of parasitoids, and the beetles (order Coleoptera), which includes at least two families, Ripiphoridae and Rhipiceridae, that are largely parasitoids, and rove beetles (family Staphylinidae) of the genus Aleochara. Occasional members of other orders can be parasitoids; one of the more remarkable is the moth family Epipyropidae, which are ectoparasitoids of planthoppers and Cicadas. The genus Cyclotorna has even more elaborate habits, beginning its growth period parasitising plant bugs, and concluding by feeding on ant larvae in their colonies.

Koinobiont parasitoid on moth larva.

Hymenopteran parasitoids often have unique life cycles. In one family, the Trigonalidae, the female wasps deposit eggs into small pockets they cut into the edge of leaves with their ovipositor. A caterpillar chewing these leaves may unknowingly swallow some of the eggs, and when they get into the caterpillar's gut, they hatch and burrow through the gut wall and into the body cavity. Later they search the caterpillar's body cavity for other parasitoid larvae, and it is these they attack and feed on. Some trigonalids, once in a caterpillar or sawfly larva, need their vehicle to fall prey to a social wasp. The wasp carries the caterpillar back to its nest, and there it is butchered and fed to the wasp's young; they will serve as the host for the trigonalid, the eggs of which are in the butchered caterpillar.

Parasitoidal and parasitic vertebrates

Perhaps because they are less specialised and their relationships with their hosts are less intimate than is the case with many invertebrates, it often is more difficult to distinguish parasitism from parasitoidy in vertebrates. In fact many of their relationships of such types do not immediately suggest parasitism to most people at all. However, the very concept is so open to interpretation that it emerges frequently in vertebrate biology.

Kleptoparasitism for example is ubiquitous, and is a major constraint on reproduction or even survival among vertebrate predators, especially in times of famine. Male lions in a pride for example, largely leave hunting for non-threatening prey to females. However, prides that specialise in very large prey such as giraffes, elephants, or buffalo, may behave differently.

Other predators such as cheetah, leopard, and even lions sometimes may be chased from their kills by hyaenas. Hyaena may sometimes follow such predators so routinely in the hope of confiscating their kills, that the hunters spend more effort on avoiding hyaena than on hunting.

Ethologists could multiply examples of kleptoparasitism many-fold; it may be intraspecific or interspecific; it ranges from the smallest foragers and predators to the largest, and may combine with predation, where the robber is happy to eat both hunter and prey. Curiously though, interspecific robbers often show at least some constraint as though they were robbing conspecifics, and do not necessarily attack the host as directly as they would have done had there not been a "robbery" situation. Interpretation and speculation about the nature of such behaviour is beyond the scope of this article however.

It is not easy to classify such relationships, because many of them involve degrees of payment in terms of protection and other benefits; for example the male lions who preempt the females' kills do at least offer protection from hyaenas and rival males.

Kleptoparasitism occurs in many other forms among vertebrates (see here for example), but for it to lead to the death of the host is not so common, and this would seem to disqualify it from the category of parasitoidy. Still, when the hosts are hard pressed in hard circumstances, the resulting injury and famine could cause reduced reproduction and even death

.

Lampreys present both parasitic and parasitoidal examples. Most species are not parasitic, but among the North American species for example, there are several species ectoparasitic on freshwater fishes. They rasp away the skin of the host and suck the blood, but most do only superficial damage. In contrast, the most notorious species is the sea lamprey, Petromyzon marinus. Its rasping wounds can extend deep into the host's flesh, and the muscle damage and loss of blood commonly weaken the host severely, affecting its reproduction unfavourably. Often the harm is severe enough to kill the host.

Hagfish, are distant relatives of lampreys. They are largely carrion feeders and predators of large worms and similar small creatures, but various species also attack weakened fishes much as some lampreys do, and accordingly rank as opportunistic parasitoids under at least some conditions.

The sabre-toothed blenny presents a curiously difficult example of parasitism to classify. It parasitises the relationship between some cleaner fish and their client fishes, more than it parasitises either party to the relationship; it attacks the client fish, approaching it in the guise of cleaner wrasse and snatches a mouthful of scales or other convenient tissue. Clients often react violently, and thereafter trust neither wrasse nor the wrasse-mimicking blenny. In its violence and the pernicious effect on a valuable relationship, it suggests parasitoidy as well as parasitism.

Another form of parasitism that can approach parasitoidy occurs in the Perissodini, Cichlids from Lake Tanganyika. Seven species in the genus Perissodus are specialised in eating scales from other fish. Their teeth are variously suited to being able to grab bits of skin with the scales attached, and such bits of skin and scale formed major components of the stomach contents. At least some of the species also have adaptations in their behavior to enable them to approach potential hosts. They also have an adaptation of the jaw that enables them to lash out sideways in passing a victim; the jaw is asymmetrical, and there is continuous selection for the asymmetry that currently is less frequent in the population, because host fishes are more alert to defend themselves on the side on which they have been attacked in the past.

Such a lifestyle is reminiscent of sharks of the genus Isistius, which is known as the Cookiecutter shark because of the circular wounds it leaves in the skins of whales and large fish that it has bitten in passing. Isistius species have been referred to as partly ectoparasitic, but they sometimes overwhelm their hosts and kill them, which by definition amounts to parasitoidy.

Candiru and related fishes in the Family Trichomycteridae, subfamilies Vandelliinae and Stegophilinae, present unusual examples of vertebrate parasitism, and occasionally parasitoidy. Most popular accounts are obsessed with the idea of candiru entering the human urethra and other orifices, but they are very varied in their habits. Some burrow partway into the skin of larger fish, apparently largely for purposes of protection and transport rather than food. Several at least are haematophagous, commonly entering the gill cavities of larger fishes and feeding on blood drawn from the gill filaments. At least when large fishes are tethered by fishermen where large numbers of the parasites occur, the hosts may die. Possibly this effect is analogous to the effect of soft ticks on hosts that do not avoid the sand patches where they assemble.

Among birds the best-known forms of parasitism are brood parasitism by various species of cuckoos, honey-guides, cowbirds, and several more. They qualify as parasitoids because many of them will cause the starvation of the host's chicks by competing with them for food, and many others either will remove host eggs when laying eggs in host nests, (sometimes eating the eggs removed), or the chick will eject or kill the eggs or chicks of the host when they hatch. Some hatchlings actually have hooked beaks adapted to attacking the host chicks and eggs, hooks that vanish before fledging.

For alternative meanings of predator and prey, see Predator (disambiguation) and Prey (disambiguation).

"Predating" can also mean "dating earlier than": see wiktionary:predate.

A South China tiger (Panthera tigris amoyensis) as the predator feeding on the blesbuck, the prey

Indian Python swallowing a small Chital deer at Mudumalai National Park

Meat ants feeding on a cicada; some species can prey on individuals of far greater size, particularly when working cooperatively

In ecology, predation describes a biological interaction where a predator (an organism that is hunting) feeds on its prey (the organism that is attacked).[1] Predators may or may not kill their prey prior to feeding on them, but the act of predation often results in the death of its prey and the eventual absorption of the prey's tissue through consumption.[2] Other categories of consumption are herbivory (eating parts of plants) and detritivory, the consumption of dead organic material (detritus). All these consumption categories fall under the rubric of consumer-resource systems.[3] It can often be difficult to separate various types of feeding behaviors.[1] For example, some parasitic species prey on a host organism and then lay their eggs on it for their offspring to feed on it while it continues to live or on its decaying corpse after it has died. The key characteristic of predation however is the predator's direct impact on the prey population. On the other hand, detritivores simply eat dead organic material arising from the decay of dead individuals and have no direct impact on the "donor" organism(s).

Selective pressures imposed on one another often leads to an evolutionary arms race between prey and predator, resulting in various antipredator adaptations. Ways of classifying predation surveyed here include grouping by trophic level or diet, by specialization, and by the nature of the predator's interaction with prey.

Functional classification

Classification of predators by the extent to which they feed on and interact with their prey is one way ecologists may wish to categorize the different types of predation. Instead of focusing on what they eat, this system classifies predators by the way in which they eat, and the general nature of the interaction between predator and prey species. Two factors are considered here: How close the predator and prey are physically (in the latter two cases the term prey may be replaced with host). Additionally, whether or not the prey are directly killed by the predator is considered, with true predation and parasitoidism involving certain death.

[edit]True predation

Predators

Leopard (Panthera pardus pardus) killing a young Bushbuck (Tragelaphus sylvaticus) in the Kruger National Park.

Lion and cub eating a Cape buffalo.

A true predator can commonly be known as one which kills and eats another organism. Whereas other types of predator all harm their prey in some way, this form certainly kills them. Predators may hunt actively for prey, or sit and wait for prey to approach within striking distance, as in ambush predators. Some predators kill large prey and dismember or chew it prior to eating it, such as a jaguar or a human; others may eat their (usually much smaller) prey whole, as does a bottlenose dolphin swallowing a fish, or a snake, duck or stork swallowing a frog. Some animals that kill both large and small prey for their size (domestic cats and dogs are prime examples) may do either depending upon the circumstances; either would devour a large insect whole but dismember a rabbit. Some predation entails venom which subdues a prey creature before the predator ingests the prey by killing, which the box jellyfish does, or disabling it, found in the behavior of the cone shell. In some cases, the venom, as in rattlesnakes and some spiders, contributes to the digestion of the prey item even before the predator begins eating. In other cases, the prey organism may die in the mouth or digestive system of the predator. Baleen whales, for example, eat millions of microscopic plankton at once, the prey being broken down well after entering the whale. Seed predation and egg predation are other forms of true predation, as seeds and eggs represent potential organisms. Predators of this classification need not eat prey entirely. For example, some predators cannot digest bones, while others can. Some may eat only part of an organism, as in grazing (see below), but still consistently cause its direct death.

[edit]Grazing

Main article: Grazing

Grazing organisms may also kill their prey species, but this is seldom the case. While some herbivores like zooplankton live on unicellular phytoplankton and have no choice but to kill their prey, many only eat a small part of the plant. Grazing livestock may pull some grass out at the roots, but most is simply grazed upon, allowing the plant to regrow once again. Kelp is frequently grazed in subtidal kelp forests, but regrows at the base of the blade continuously to cope with browsing pressure. Animals may also be 'grazed' upon; female mosquitos land on hosts briefly to gain sufficient proteins for the development of their offspring. Starfish may be grazed on, being capable of regenerating lost arms.

[edit]Parasitism

Main article: Parasitism

Parasites can at times be difficult to distinguish from grazers. Their feeding behavior is similar in many ways, however they are noted for their close association, with their host species. While a grazing species such as an elephant may travel many kilometers in a single day, grazing on many plants in the process, parasites form very close associations with their hosts, usually having only one or at most a few in their lifetime. This close living arrangement may be described by the term symbiosis, "living together", but unlike mutualism the association significantly reduces the fitness of the host. Parasitic organisms range from the macroscopic mistletoe, a parasitic plant, to microscopic internal parasites such as cholera. Some species however have more loose associations with their hosts. Lepidoptera (butterfly and moth) larvae may feed parasitically on only a single plant, or they may graze on several nearby plants. It is therefore wise to treat this classification system as a continuum rather than four isolated forms.

[edit]Parasitoidism

Main article: Parasitoid

Parasitoids are organisms living in or on their host and feeding directly upon it, eventually leading to its death. They are much like parasites in their close symbiotic relationship with their host or hosts. Like the previous two classifications parasitoid predators do not kill their hosts instantly. However, unlike parasites, they are very similar to true predators in that the fate of their prey is quite inevitably death. A well known example of a parasitoids are the ichneumon wasps, solitary insects living a free life as an adult, then laying eggs on or in another species such as a caterpillar. Its larva(e) feed on the growing host causing it little harm at first, but soon devouring the internal organs until finally destroying the nervous system resulting in prey death. By this stage the young wasp(s) are developed sufficiently to move to the next stage in their life cycle. Though limited mainly to the insect order Hymenoptera, Diptera and Coleoptera parasitoids make up as much as 10% of all insect species.[4][5]

[edit]Degree of specialization

Further information: Generalist and specialist species

An opportunistic Alligator swims with a deer.

Among predators there is a large degree of specialization. Many predators specialize in hunting only one species of prey. Others are more opportunistic and will kill and eat almost anything (examples: humans, leopards, and dogs). The specialists are usually particularly well suited to capturing their preferred prey. The prey in turn, are often equally suited to escape that predator. This is called an evolutionary arms race and tends to keep the populations of both species in equilibrium. Some predators specialize in certain classes of prey, not just single species. Some will switch to other prey (with varying degrees of success) when the preferred target is extremely scarce, and they may also resort to scavenging or a herbivorous diet if possible.[citation needed]

[edit]Trophic level

Mantis (Tenodera aridifolia) eating a bee.

See also: Trophic level and Trophic dynamics

Predators are often another organism's prey, and likewise prey are often predators. Though blue jays prey on insects, they may in turn be prey for cats and snakes, which, in the latter's case, may themselves be the prey of hawks. One way of classifying predators is by trophic level. Organisms which feed on autotrophs, the producers of the trophic pyramid, are known as herbivores or primary consumers; those that feed on heterotrophs such as animals are known as secondary consumers. Secondary consumers are a type of carnivore, but there are also tertiary consumers eating these carnivores, quartary consumers eating them, and so forth. Because only a fraction of energy is passed on to the next level, this hierarchy of predation must end somewhere, and very seldom goes higher than five or six levels, and may go only as high as three trophic levels (for example, a lion that preys upon large herbivores such as wildebeest which in turn eat grasses). A predator at the top of any food chain (that is, one that is preyed upon by no organism) is called an apex predator; examples include the orca, sperm whale, anaconda, Komodo dragon, tiger, lion, tiger shark, Nile crocodile, and most eagles -- and even omnivorous humans and grizzly bears. An apex predator in one environment may not retain this position as a top predator if introduced to another habitat, such as a dog among alligators or a snapping turtle among jaguars; a predatory species introduced into an area where it faces no predators, such as a domestic cat or a dog in some insular environments, can become an apex predator by default.

Many organisms (of which humans are prime examples) eat from multiple levels of the food chain and thus make this classification problematic. A carnivore may eat both secondary and tertiary consumers, and its prey may itself be difficult to classify for similar reasons. Organisms showing both carnivory and herbivory are known as omnivores. Even herbivores such as the giant panda may supplement their diet with meat. Scavenging of carrion provides a significant part of the diet of some of the most fearsome predators. Carnivorous plants would be very difficult to fit into this classification, producing their own food but also digesting anything that they may trap. Organisms which eat detritivores or parasites would also be difficult to classify by such a scheme.

[edit]Predation as competition

An alternative view offered by Richard Dawkins is of predation as a form of competition: the genes of both the predator and prey are competing for the body (or 'survival machine') of the prey organism.[6] This is best understood in the context of the gene centered view of evolution. Another manner in which predation and competition are connected is throughout intraguild predation. Intraguild predators are those that kill and eat other predators of different species at the same trophic level, and thus that are potential competitors.[7]

[edit]Ecological role

Predators may increase the biodiversity of communities by preventing a single species from becoming dominant. Such predators are known as keystone species and may have a profound influence on the balance of organisms in a particular ecosystem. Introduction or removal of this predator, or changes in its population density, can have drastic cascading effects on the equilibrium of many other populations in the ecosystem. For example, grazers of a grassland may prevent a single dominant species from taking over.[8]

The elimination of wolves from Yellowstone National Park had profound impacts on the trophic pyramid. Without predation, herbivores began to over-graze many woody browse species, affecting the area's plant populations. Additionally, wolves often kept animals from grazing in riparian areas, which protected beavers from having their food sources encroached upon. The removal of wolves had a direct effect on beaver populations, as their habitat became territory for grazing.[9] Furthermore, predation keeps hydrological features such as creeks and streams in normal working order. Increased browsing on willows lenr and conifers along Blacktail Creek due to a lack of predation resulted in channel incision because those species helped slow the water down and hold the soil in place.[9]

[edit]Adaptations and behavior

The act of predation can be broken down into a maximum of four stages: Detection of prey, attack, capture and finally consumption.[10] The relationship between predator and prey is one which is typically beneficial to the predator, and detrimental to the prey species. Sometimes, however, predation has indirect benefits to the prey species,[11] though the individuals preyed upon themselves do not benefit.[12] This means that, at each applicable stage, predator and prey species are in an evolutionary arms race to maximize their respective abilities to obtain food or avoid being eaten. This interaction has resulted in a vast array of adaptations in both groups.

Camouflage of the dead leaf mantis makes it less visible to both its predators and prey.

One adaptation helping both predators and prey avoid detection is camouflage, a form of crypsis where species have an appearance which helps them blend into the background. Camouflage consists of not only color, but also shape and pattern. The background upon which the organism is seen can be both its environment (e.g. the praying mantis to the right resembling dead leaves) or other organisms (e.g. zebras' stripes blend in with each other in a herd, making it difficult for lions to focus on a single target). The more convincing camouflage is, the more likely it is that the organism will go unseen.

Mimicry in Automeris io.

Mimicry is a related phenomenon where an organism has a similar appearance to another species. One such example is the drone fly, which looks a lot like a bee, yet is completely harmless as it cannot sting at all. Another example of batesian mimicry is the io moth, (Automeris io), which has markings on its wings which resemble an owl's eyes. When an insectivorous predator disturbs the moth, it reveals its hind wings, temporarily startling the predator and giving it time to escape. Predators may also use mimicry to lure their prey, however. Female fireflies of the genus Photuris, for example, copy the light signals of other species, thereby attracting male fireflies which are then captured and eaten (see aggressive mimicry).[13]

[edit]Predator

A juvenile Red-tailed Hawk eating a California vole

Great blue heron with prey.

Lizard with prey.

While successful predation results in a gain of energy, hunting invariably involves energetic costs as well. When hunger is not an issue, most predators will generally not seek to attack prey since the costs outweigh the benefits. For instance, a large predatory fish like a shark that is well fed in an aquarium will typically ignore the smaller fish swimming around it (while the prey fish take advantage of the fact that the apex predator is apparently uninterested). Surplus killing represents a deviation from this type of behaviour. The treatment of consumption in terms of cost-benefit analysis is known as optimal foraging theory, and has been quite successful in the study of animal behavior. Costs and benefits are generally considered in energy gain per unit time, though other factors are also important, such as essential nutrients that have no caloric value but are necessary for survival and health.

Social predation offers the possibility of predators to kill creatures larger than those that members of the species could overpower singly. Lions, hyenas, wolves, dholes, African wild dogs, and piranhas can kill large herbivores that single animals of the same species could never dispatch. Social predation allows some animals to organize hunts of creatures that would easily escape a single predator; thus chimpanzees can prey upon colobus monkeys, and Harris's Hawks can cut off all possible escapes for a doomed rabbit. Extreme specialization of roles is evident in some hunting that requires co-operation between predators of very different species: humans with the aid of falcons or dogs, or fishing with cormorants or dogs. Social predation is often very complex behavior, and not all social creatures (for example, domestic cats) perform it. Even without complex intelligence but instinct alone, some ant species can destroy much-larger creatures.

Size-selective predation involves predators preferring prey of a certain size. Large prey may prove troublesome for a predator, while small prey might prove hard to find and in any case provide less of a reward. This has led to a correlation between the size of predators and their prey.[14] Size may also act as a refuge for large prey, for example adult elephants are generally safe from predation by lions, but juveniles are vulnerable.[14]

It has been observed that well-fed predator animals in a lax captivity (for instance, pet or farm animals) will usually differentiate between putative prey animals who are familiar co-inhabitants in the same human area from wild ones outside the area. This interaction can range from peaceful coexistence to close companionship; motivation to ignore the predatory instinct may result from mutual advantage or fear of reprisal from human masters who have made clear that harming co-inhabitants will not be tolerated. Pet cats and pet mice, for example, may live together in the same human residence without incident as companions. Pet cats and pet dogs under human mastership often depend on each other for warmth, companionship, and even protection, particularly in rural areas.

[edit]Antipredator adaptations

Main article: Antipredator adaptation

Antipredator adaptations have evolved in prey populations due to the selective pressures of predation over long periods of time.

[edit]Aggression

Predatory animals often use their usual methods of attacking prey to inflict or to threaten grievous injury to their own predators. The electric eel uses the same electrical current to kill prey and to defend itself against animals (anacondas, caimans, jaguars, egrets, cougars, giant otters, humans, and dogs) that ordinarily prey upon fish similar to an electric eel in size; the electric eel thus remains an apex predator in a predator-rich environment. A predator small enough to be prey for others, the domestic cat uses its formidable teeth and claws as weapons against animals that might confuse a cat with easier prey. Many non-predatory prey animals, such as a zebra, can give a strong kick that can maim or kill, while others charge with tusks or horns.

[edit]Mobbing behavior

Main article: Mobbing behavior

Mobbing behavior occurs when members of a species drive away their predator by cooperatively attacking or harassing it. Most frequently seen in birds, mobbing is also seen in other social animals. For example, nesting gull colonies are widely seen to attack intruders, including humans.[10] Costs of mobbing behavior include the risk of engaging with predators, as well as energy expended in the process, but it can aid the survival of members of a species.

While mobbing has evolved independently in many species, it tends to be present only in those whose young are frequently preyed on, especially birds. It may complement cryptic behavior in the offspring themselves, such as camouflage and hiding. Mobbing calls may be made prior to or during engagement in harassment.

Mobbing can be an interspecies activity: it is common for birds to respond to mobbing calls of a different species. Many birds will show up at the sight of mobbing and watch and call, but not participate. It should also be noted that some species can be on both ends of a mobbing attack. Crows are frequently mobbed by smaller songbirds as they prey on eggs and young from these birds' nests, but these same crows will cooperate with smaller birds to drive away hawks or larger mammalian predators. On occasion, birds will mob animals that pose no threat.

[edit]Advertising unprofitability

Thomson's gazelles exhibit stotting behavior.

A Thomson's gazelle seeing a predator approach may start to run away, but then slow down and stot. Stotting is jumping into the air with the legs straight and stiff, and the white rear fully visible. Stotting is maladaptive for outrunning predators; evidence suggests that stotting signals an unprofitable chase. For example, cheetahs abandon more hunts when the gazelle stots, and in the event they do give chase, they are far less likely to make a kill.[15]

Aposematism, where organisms are brightly colored as a warning to predators, is the antithesis of camouflage. Some organisms pose a threat to their predators—for example they may be poisonous, or able to harm them physically. Aposematic coloring involves bright, easily recognizable and unique colors and patterns. Upon being harmed (e.g., stung) by their prey, the appearance in such an organism will be remembered as something to avoid. While that particular prey organism may be killed, the coloring benefits the prey species as a whole.

Domestic cats, animals similar in size to such prey species as rabbits, make a hissing sound reminiscent of a snake, advertising that they can put up formidable defenses for their size. Such can deter confrontations harmful to both the cat and to an animal in search of small animals as prey.

[edit]Chemical defense

Main article: Chemical defense

Some organisms have evolved chemical weapons which are effective deterrents against predation. It is most common in insects, but the skunk is a particularly dramatic mammalian example. Other examples include the Bombardier beetle which can accurately shoot a predator with a stream of boiling poison, the Ornate moth which excretes a frothy alkaloid mixture, and the Pacific beetle cockroach sprays a quinone mixture from modified spiracles.

[edit]Terrain Fear Factor

The "terrain fear factor" is an idea which assesses the risks associated with predator/prey encounters. This idea suggests that prey will change their usual habits to adjust to the terrain and its effect on the species' predation. For example, a species may forage in a terrain with a lower predation risk as opposed to one with high predation risk.[16]

[edit]Population dynamics

It is fairly clear that predators tend to lower the survival and fecundity of their prey, but on a higher level of organization, populations of predator and prey species also interact. It is obvious that predators depend on prey for survival, and this is reflected in predator populations being affected by changes in prey populations. It is not so obvious, however, that predators affect prey populations.[17] Eating a prey organism may simply make room for another if the prey population is approaching its carrying capacity.

The population dynamics of predator-prey interactions can be modelled using the Lotka–Volterra equations. These provide a mathematical model for the cycling of predator and prey populations. Predators tend to select young, weak, and ill individuals.[18]

[edit]Evolution of predation

Predation appears to have become a major selection pressure shortly before the Cambrian period—around 550 million years ago—as evidenced by the almost simultaneous development of calcification in animals and algae,[19] and predation-avoiding burrowing. However, predators had been grazing on micro-organisms since at least 1,000 million years ago.[20][20][21][22][23]

[edit]Humans and predation

[edit]As predators

Humans are omnivorous. They hunt and trap animals using weapons and tools like snares, clubs, spears, fishing gear, firearms to boats and motor vehicles. Humans even use other predatory species, (such as dogs, cormorants, and falcons) in hunting and fishing; some people even enlist such non-predatory beasts, like horses, camels, and elephants in getting approaches to prey.

Humans have reshaped huge expanses of the world as ranges and farms for the raising of livestock, poultry, and fish to be eaten as meat. However, it can be debated whether or not harvesting livestock fits strictly in the definition of predation.

Human raising and eating of livestock is part of agriculture, and involves the feeding of and caring for animals, followed by their being slaughtered with an appropriate tool, cutting up, and cooking. In many cultures, animals are hunted or farmed by specialists (such as ranchers or fishermen), brought to a marketplace, and sold in pieces to the people who actually consume the meat.

[edit]As prey

Signage in Addo Elephant National Park reminding humans as to their status of prey.

A lone naked human is at a physical disadvantage to other comparable apex predators in areas such as speed, bone density, weight, and physical strength. Humans also lack innate weaponry such as claws. Without crafted weapons, society, or cleverness, a lone human can easily be defeated by fit predatory animals, such as wild dogs, big cats and bears. There are even recorded instances of lone humans being preyed upon by large carnivores (see Man-eater). However, humans are not solitary creatures; they are social animals with highly developed social behaviors. Further, humans and their ancestors (such as Homo erectus) have been using stone tools and weapons for well over a million years. Anatomically modern humans have been apex predators since they first evolved, and many species of carnivorous megafauna actively avoid interacting with humans; the primary environmental competitor for a human is other humans. The one subspecies of carnivorous megafauna that does interact frequently with humans in predatory roles is the domestic dog, but usually as a partner in predation especially if they hunt together. Cannibalism has occurred in various places, among various cultures, and for various reasons. At least a few people, such as the Donner party, are said to have resorted to it in desperation.

[edit]In conservation

Predators are an important consideration in matters relating to conservation. In many cases, the predators are not only apex predators, but are also endangered species themselves as they have lower population sizes than prey species and are much more vulnerable to extinction because of their population size, competition with other predators, and the fluctuations in prey populations.

Having small population size is a characteristic almost universally inherent to apex predators. Low numbers wouldn't be a problem for apex predators if there was an abundance of prey and no competition or niche overlap, a scenario that is rarely- if ever- encountered in the wild. The competitive exclusion principle states that if two species' ecological niches overlap, there is a very high likelihood of competition as both species are in direct competition for the same resources. This factor alone could lead to the extirpation of one or both species, but is compounded by the added factor of prey abundance.

A predator's effect on its prey species is hard to see in the short-term. However, if observed over a longer period of time, it is seen that the population of a predator will correlationally rise and fall with the population of its prey in a cycle similar to the boom and bust cycle of economics. If a predator overhunts its prey, the prey population will lower to numbers that are too scarce for the predators to find. This will cause the predator population to dip, decreasing the predation pressure on the prey population. The decrease in predators will allow the small number of prey left to slowly increase their population to somewhere around their previous abundance, which will allow the predator population to increase in response to the greater availability of resources. If a predator hunts its prey species to numbers too low to sustain the population in the short term, they can cause not only the extinction or extirpation of the prey, but also the extinction of their own species, a phenomenon known as coextinction. This is a risk that wildlife conservationists encounter when introducing predators to prey that have not coevolved with the same or similar predators. This possibility depends largely on how well and how fast the prey species is able to adapt to the introduced predator. One way that this risk can be avoided is if the predator finds an alternative prey species or if an alternative prey species is introduced (something that ecologists and environmentalists try to avoid whenever possible). An alternative prey species would help to lift some of the predation pressure from the initial prey species, giving the population a chance to recover, however it does not guarantee that the initial prey species will be able to recover as the initial prey population may have been hunted to below sustainable numbers or to complete extinction.

[edit]Biological pest control

Main article: Biological pest control

Predators may be put to use in conservation efforts to control introduced species. Although the aim in this situation is to remove the introduced species entirely, keeping its abundance down is often the only possibility. Predators from its natural range may be introduced to control populations, though in some cases this has little effect, and may even cause unforeseen problems. Besides their use in conservation biology, predators are also important for controlling pests in agriculture. Natural predators are an environmentally friendly and sustainable way of reducing damage to crops, and are one alternative to the use of chemical agents such as pesticides.